/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.matheclipse.core.stat.descriptive.summary;

import java.io.Serializable;

import org.matheclipse.core.expression.F;
import org.matheclipse.core.interfaces.IAST;
import org.matheclipse.core.interfaces.IExpr;
import org.matheclipse.core.stat.descriptive.AbstractSymbolicStorelessUnivariateStatistic;

/**
 * Returns the sum of the natural logs for this collection of values.
 * <p>
 * Therefore,
 * <ul>
 * <li>If any of values are &lt; 0, the result is <code>NaN.</code></li>
 * <li>If all values are non-negative and less than
 * <code>Double.POSITIVE_INFINITY</code>, but at least one value is 0, the
 * result is <code>Double.NEGATIVE_INFINITY.</code></li>
 * <li>If both <code>Double.POSITIVE_INFINITY</code> and
 * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is
 * <code>NaN.</code></li>
 * </ul>
 * </p>
 * <p>
 * <strong>Note that this implementation is not synchronized.</strong> If
 * multiple threads access an instance of this class concurrently, and at least
 * one of the threads invokes the <code>increment()</code> or
 * <code>clear()</code> method, it must be synchronized externally.
 * </p>
 * 
 */
public class SymbolicSumOfLogs extends AbstractSymbolicStorelessUnivariateStatistic implements Serializable {

	/** Serializable version identifier */
	private static final long serialVersionUID = -370076995648386763L;

	/** Number of values that have been added */
	private int n;

	/**
	 * The currently running value
	 */
	private IExpr value;

	/**
	 * Create a SumOfLogs instance
	 */
	public SymbolicSumOfLogs() {
		value = F.C0;
		n = 0;
	}

	/**
	 * Copy constructor, creates a new {@code SumOfLogs} identical to the {@code
	 * original}
	 * 
	 * @param original
	 *          the {@code SumOfLogs} instance to copy
	 */
	// public SumOfLogs(SumOfLogs original) {
	// copy(original, this);
	// }

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void increment(final IExpr d) {
		value = F.eval(F.Plus(value, F.Log(d)));
		n++;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public IExpr getResult() {
		return value;
	}

	/**
	 * {@inheritDoc}
	 */
	public long getN() {
		return n;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void clear() {
		value = F.C0;
		n = 0;
	}

	/**
	 * Returns the sum of the natural logs of the entries in the specified portion
	 * of the input array, or <code>Double.NaN</code> if the designated subarray
	 * is empty.
	 * <p>
	 * Throws <code>IllegalArgumentException</code> if the array is null.
	 * </p>
	 * <p>
	 * See {@link SymbolicSumOfLogs}.
	 * </p>
	 * 
	 * @param values
	 *          the input array
	 * @param begin
	 *          index of the first array element to include
	 * @param length
	 *          the number of elements to include
	 * @return the sum of the natural logs of the values or 0 if length = 0
	 * @throws IllegalArgumentException
	 *           if the array is null or the array index parameters are not valid
	 */
	@Override
	public IExpr evaluate(final IAST values, final int begin, final int length) {

		if (test(values, begin, length, true)) {
			IAST sumLog = F.Plus();
			for (int i = begin; i < begin + length; i++) {
				sumLog.add(F.Log(values.get(i)));
			}
			if (sumLog.size() > 1) {
				return F.eval(sumLog);
			}
		}

		return null;
	}
	// /**
	// * {@inheritDoc}
	// */
	// @Override
	// public SumOfLogs copy() {
	// SumOfLogs result = new SumOfLogs();
	// copy(this, result);
	// return result;
	// }
	//
	// /**
	// * Copies source to dest.
	// * <p>Neither source nor dest can be null.</p>
	// *
	// * @param source SumOfLogs to copy
	// * @param dest SumOfLogs to copy to
	// * @throws NullArgumentException if either source or dest is null
	// */
	// public static void copy(SumOfLogs source, SumOfLogs dest)
	// throws NullArgumentException {
	// MathUtils.checkNotNull(source);
	// MathUtils.checkNotNull(dest);
	// dest.setData(source.getDataRef());
	// dest.n = source.n;
	// dest.value = source.value;
	// }
}
